1. Field of the Invention
The present invention is in the field of fruit ripening methods and apparatus, and the invention relates more particularly to methods and apparatus involving an artificially prepared atmosphere containing a small proportion of ethylene gas.
2. Description of the Prior Art
There has been a long-felt need for a method and apparatus capable of accelerating the ripening cycle of fruit to a shortened period of time such as only about 48 hours so that the availability of fully ripened fruit could be closely coordinated to marketing or user's requirements. This need has been in at least three areas: (1) at the commercial level in both packing houses and wholesaler's storage facilities; (2) also at the commercial level at markets, hotels and restaurants; and (3) in the home.
For many years there have been attempts to ripen fruit in a "banana" room, where the fruit to be ripened was placed in the same room as already ripe bananas which, during the ripening process, naturally gave off ethylene gas. However, carbon dioxide, which is a natural inhibitor of the ripening process, was also given off during the ripening of both the fruit being treated and the bananas, so that results were generally unsatisfactory. The density of carbon dioxide is more than four-thirds that of air and ethylene gas, so that carbon dioxide accumulated in the lower part of the ripening room, with the result that there was often little or no ripening of the lowermost fruit. While at least some of this accumulated carbon dioxide was accidentally released when the doors of the ripening room were opened, such occasional and accidental release of carbon dioxide was insufficient to avoid the retarding effects of carbon dioxide on the ripening cycle.
A home fruit ripening unit has been recently marketed in the United States which utilizes the same basic principle of operation as the "banana room," and this home ripening unit is generally ineffective for the same reasons. This home unit is generally in the form of a covered bowl in which already ripe or overripe fruit is placed in a lower portion, and the fruit to be ripened in an upper portion so as to be subjected to the ethylene gas given off by the already ripe fruit. The problem here, again, is that accumulating carbon dioxide caused by the ripening process is a barrier to proper ripening of the lower portion of the fruit, and the result is that while some of the fruit may be ripened, some of it may not be, and some may have portions thereof which are both ripened and unripened.
A more modern system for ripening fruit on a commercial scale which is presently sometimes used involves placing fruit in a packing house room or wholesale storage room, introducing ethylene gas into the room, and allowing the proportion of ethylene gas to rise to a level of about 500 to 1,000 parts per million, and then allowing the fruit to absorb the ethylene gas over a ripening period of a day or two. The problem with this system is that because of carbon dioxide accumulation in the room, it is necessary every 2-4 hours to open the doors and flush the air and carbon dioxide out of the room, and then to close the doors again and rebuild the ethylene gas concentration back up to the approximately 500 to 1,000 parts per million. This sequence had to be repeated over the entire length of the ripening period, and the resulting requirement of constant maintenance over the entire ripening period renders the entire system impractical. Also, this procedure of opening the doors of the room to release carbon dioxide and air and then replacing the air and ethylene gas was not a really effective way of removing the carbon dioxide, and the lower lugs of fruit were usually in carbon dioxide anyway to the extent that they did not ripen effectively.
Such ripening procedures have been haphazard at best, and have not utilized critical parameters of ripening temperature, ethylene gas concentration, duration of exposure to ethylene gas, and minimum allowable carbon dioxide concentration, all of which must be adhered to in order to have an effective fruit ripening process.
Most fruit must be picked and shipped green or unripened because of shipping problems with ripe fruit. Then, a ripening period of time generally on the order of two or three weeks must be awaited before the fruits are ready for consumption. Such ripening period of time is even longer for avocados and several other fruits because the enzymic action necessarily associated with ripening will not normally commence until 5-7 days after picking. Storage of the fruit at the wholesaler's, market, hotel, restaurant, or the like over the accumulated ripening period of time occupies valuable space, and it is extremely difficult to coordinate ripening times and market demands, particularly for fruit such as the avocado which is quite delicate and also has an extended ripening time.
While this problem of coordinating ripening time and market needs is largely solved by the present invention, there is another problem of storage facilities required for ripening that is peculiar to the avocado industry. Partly because of the fragility of the avocado, there are always a large number of avocados in any batch that are visually unacceptable for the commercial market as whole fruit because of cuts, scars and other deformities. These are still usable to make guacamole, but heretofore they have occupied valuable storage space for the extended period of time required for the natural ripening process to occur before they could be processed as guacamole. The need for such additional storage space and time could be virtually completely eliminated by a practical and reliable artificial system such as that of the present invention.